1. Field of the Invention
This invention relates to an inkjet printing apparatus for performing printing by moving a printing medium relative to inkjet heads.
2. Description of the Related Art
What is called a one-pass inkjet printing apparatus is known as an inkjet printing apparatus for outputting a large number of prints at high speed. This printing apparatus includes a print head having a plurality of inkjet heads to secure a discharge range substantially corresponding to a width in a primary scanning direction perpendicular to a transport direction of a recording medium (secondary scanning direction), and carries out recording by discharging ink as necessary to the recording medium transported.
In such an inkjet printing apparatus, head caps are used for the purpose of preventing drying of the inkjet heads. In order to prevent drying and contamination of areas adjacent ink discharge portions of the inkjet heads, these head caps cap (or cover) the areas adjacent the ink discharge portions of the inkjet heads during a printing standby time.
At a time of printing, such head caps need to be moved to a withdrawn position not to interfere with the printing. Japanese Unexamined Patent Publication No. 2008-55891 discloses an image forming apparatus having a cap member for enclosing a print head, in which the cap member is moved to a withdrawn position by means of a pivotable holding lever.
Where a construction as described in the above Japanese publication is employed to move head caps, as they are, laterally of the inkjet heads by using the holding lever, a large space is required to secure a moving area and a withdrawn area for the head caps. This gives rise to a problem of requiring a large space occupied by the entire inkjet printing apparatus. Particularly where, in order to perform efficient printing, a plurality of inkjet head rows, each row including a plurality of inkjet heads arranged in the primary scanning direction, are arranged in the transport direction of printing paper (secondary scanning direction), a head cap holder supporting the head caps will have a large area, thereby requiring a further enlarged space.
In such an inkjet printing apparatus, ink mist produced by ink scattering at a time of discharge, and paper powder produced from printing paper which is a recording medium, could adhere to ink discharge nozzle forming surfaces of the inkjet heads, thereby causing a defective ink discharge from the ink discharge nozzles. In order to maintain printing quality, therefore, such an inkjet printing apparatus includes a mechanism for cleaning the inkjet heads when necessary.
Japanese Unexamined Patent Publication No. 2001-18406 discloses an inkjet printing apparatus including a wiper carrier reciprocable in the primary scanning direction of a nozzle head having numerous inkjet nozzles aligned in the primary scanning direction. This inkjet printing apparatus, after forcibly discharging ink from the nozzle heads positioned in a maintenance position, changes the position of the nozzle heads to a nozzle head wiping position, and moves the wiper carrier in one direction. Then, nozzle head wipers attached to an upper portion of the wiper carrier are placed in contact with forward ends (lower ends) of the nozzle heads to wipe away the ink adhering to the nozzle heads.
However, the inkjet printing apparatus disclosed in Japanese Unexamined Patent Publication No. 2001-18406 goes through a complicated operation to move the nozzle heads to the nozzle head wiping position, then move the nozzle heads upward to an ink receiving member wiping position, and further return the nozzle heads to a printing position. This poses a problem in that the construction around the nozzle heads becomes complicated.
When, for example, a maintenance operation is carried out before starting printing by the inkjet printing apparatus, the nozzle heads kept on standby in the maintenance position which is a non-printing position are moved to the nozzle head wiping position above, and moved to the ink receiving member wiping position still above. After a wiping operation there, the nozzle heads are moved to the printing position. That is, the nozzle heads undergo a complicated operation to move upward, then move further upward and thereafter descend to a lowermost position. When the nozzle heads are put on standby in the maintenance position after the nozzles are wiped upon completion of printing by the inkjet printing apparatus, the nozzle heads similarly undergo a complicated operation to move upward, then move further upward and thereafter descend to the lowermost position. Such positioning operation is inefficient, and the construction around the nozzle heads also becomes complicated.
It is desirable that the wipers for wiping the ink discharge nozzles have the least chance of damage through friction. For this purpose, a mechanism is required for allowing the wipers to contact only the smooth inkjet heads, without contacting a component which supports the inkjet heads.
In addition, it is necessary to clean the wipers per se as necessary since ink accumulates on the wipers through operations for wiping the ink discharge heads.
Further, in such an inkjet printing apparatus, an ink storage tank is divided into a main tank and a subtank, and the subtank is disposed on an ink flow path between the main tank and inkjet heads. The ink is fed to the inkjet heads through this subtank. This is because, when an ink tank and the inkjet heads are directly connected without providing a subtank, there arises a problem of failing to discharge the ink steadily from the inkjet heads due to an amount of ink stored in the ink tank and other factors.
In the conventional inkjet printing apparatus, the subtank is fixed, separately from the inkjet heads, to the outside of an inkjet head holder holding the inkjet heads. On the other hand, the inkjet heads are movable up and down in order to perform a printing operation and a maintenance operation, which results in a difference in height between the inkjet heads and subtank. The difference in height between the inkjet heads and subtank spoils the meniscus of the ink in the inkjet heads. This makes an accurate discharge of ink impossible, and causes printing failures such as missing nozzle.
Japanese Unexamined Patent Publication No. 2004-358946 discloses an inkjet printing apparatus which moves an intermediate tank up and down to vary its height relative to a recording head and control ink back pressure of the recording head, thereby to improve a degree of freedom for arranging the intermediate tank and a main tank, and also realize space-saving. However, changing the height of the intermediate tank gives rise to a problem of making control of the ink discharge difficult, and only making uniform ink discharge impossible.